1. Field of the Invention
The present invention relates to an image display apparatus and an image erasing method, in which a color image made of an ink can be displayed on a recording medium by fixing the ink on the recording medium, and, when it is desired to erase the color image, the color image on the recording medium can be erased by image erasing means.
2. Related Background Art
In recent years, as global environment problems, attention is attracted to the reduction of the waste and the resource usage, and important task is to reduce the waste of recording media, such as papers, plastic films for overhead projector (OHP) and the like, as well as the usage of the materials for the recording media, such as wood resources, petroleum and the like. As a part of measures to the reduction of the resource usage, the reuse of the papers and the like as waste papers, which are used once, without disposal of them is progressing. However, the plastic films for OHP and the like are almost not recovered, and further, there are many problems about the recovery and reuse of these films. Specifically, for example, with respect to the recovery, there are problems about the labor for the dividing operation in accordance with the types of the recording media and the operation cost required for the recovery, as well as the collection place and the control for the recovered materials. With respect to the reuse, there are problems about the quality of the reproduced products and the cost required for the deinking treatment of the ink and the like.
An information board or an electronic blackboard is an image display device which has solved the above-mentioned problems. Specifically, this image display device is a device in which the image recorded once on the recording medium can be erased, an image can be recorded on the recording medium repeatedly, and the image recorded can be erased repeatedly. Such an image display device is one which is effective for the resource-saving because a recording medium is not consumed uselessly, and utilized for various purposes.
In general, an information board or an electronic blackboard is an image display device for displaying a static image on a large display. The information board is an image display device for displaying the image formed by an input device, such as a computer or the like, on a recording medium, mainly for the purpose of advertisement, propaganda, notice and the like. For example, this is a device which functions as a guide plate, in station precincts, for displaying information, such as the destination of a train, the operation state and the like; functions as a program table, at the entrance of a meeting room and in a wedding hall, for displaying the program; and functions as a notice plate, in a university, for displaying information, such as cancellation of lectures, changing of a lecture room and the like. Further, the electronic blackboard is a device used in a conference, a meeting or the like, in which an image, such as a character, a figure or the like, written on a recording medium (hereinafter, referred to also as display sheet) is read by a scanner and copied, and then, the image can be erased by means of a blackboard eraser.
Herein, the above-mentioned information board and electronic blackboard are explained in detail.
First, with respect to the information board, in the conventional information board in which a static image is recorded and displayed on the recording medium and erased as mentioned above, a toner image is formed by allowing a conductive magnetic toner to electrostatically adsorb onto an endless sheet (recording medium) in a belt form utilizing a magnestylus technique. The toner image is displayed by moving the sheet, and, after the display, the toner image is erased by removing the static electricity between the toner and the sheet.
FIG. 11 is a cross-sectional view of the conventional information board. In addition, FIG. 12 is a partially sectional view of the recording medium used in the conventional information board. Using FIG. 11 and FIG. 12, the conventional information board is explained.
In FIG. 11, 801 designates a recording electrode, 802 designates a conductive magnetic toner, and 803 designates a recording medium. Recording medium 803, as shown in FIG. 12, comprises surface dielectric layer 901a, resistance layer 901b, conductive layer 901c, and supporting layer 901d. 
Further, in FIG. 11, 804 designates an image formation unit, 805 designates a circuit substrate, 806 designates a cleaning brush, 807 designates a rotation magnet, 808 designates a non-magnetic cylinder, 809 designates a movement roller for moving the recording medium, 810 designates a display window, and 811 designates a body frame.
Thus, in this information board, by rotating the above-mentioned rotation magnet 807, conductive magnetic toner 802 as a colorant substance is conveyed on the above-mentioned non-magnetic cylinder 808, so that this is supplied on recording electrode 801 composed of a magnetic substance. Then, a voltage corresponding to the image signal generated by circuit substrate 805 is applied between conductive layer 901c of recording medium 803 and recording electrode 801, and by the electric charge (10xe2x88x928 to 10xe2x88x927 c) induced in toner 802, the above toner 802 is allowed to electrostatically adhere to recording medium 803 (1,000 to 10,000 pF/cm2), to thereby form an image. It is noted that the image formed once is returned to the original position by rotating recording medium 803 in the form of an endless belt by one cycle, and toner 802 is scraped down from recording medium 803 by cleaning brush 806 and recovered on the above-mentioned recording electrode 801 which is set immediately below brush 806, so that recording medium 803 is reused.
Such an information board can perform the image writing and erasing in accordance with the image information transmitted from an external image input device, such as a computer or the like. Further, by connecting the external image input device with each information board through a network, it becomes possible to display the image information transmitted from the external image input device on each information board in a distant place simultaneously, and the information board can be effectively utilized as a display device for the notice plate, advertisement plate and the like.
Next, an electronic blackboard is explained. FIGS. 13A to 13C are diagrammatic views showing the construction of the conventional electronic blackboard, and FIG. 13A is a top view, FIG. 13B is a front view, and FIG. 13C is a side view.
As shown in those drawings, in this electronic blackboard, within leg-fitted box type frame 1001 having, at the front, opening 1001a in a rectangular form, recording medium (display sheet) 1002 to be a display surface is arranged in a state such that it is built over right and left rollers 1003, 1004. On the surface of this display sheet 1002, using a pen containing an exclusive ink, not only can an optional image, such as a character, a figure or the like, be written in handwriting, but also the image can be erased by a blackboard eraser, and further, the writing and the erasing can be repeated endlessly. Further, this display sheet 1002 is endlessly scanned by rotating one roller 103 using the driving device, which is not shown.
In addition, at the rear of one roller 1003 in the above-mentioned box type frame 1001, there is arranged display surface image reading scanner 1005 which covers the entire of the width of display sheet 1002 (length in the direction perpendicular to the moving direction) and is capable of reading the image on display sheet 1002.
Further, at the lower portion of the above-mentioned box type frame 1001, there is arranged printer 1006 which performs the printing of the image on display sheet 1002 read by the above-mentioned display surface image reading scanner 1005 on a paper surface.
When the printing is performed by this printer 1006, the image on display sheet 1002 is read by display surface image reading scanner 1005 by moving display sheet 1002. Thus, display surface image reading scanner 1005 successively reads the image according to the movement of display sheet 1002 and transmits the image data in the form of an electric signal to printer 1006 successively. Then, printer 1006 performs the printing of the image on display sheet 1002 in accordance with the image data from display surface image reading scanner 1005 on a paper surface.
Thus, the above-mentioned electronic blackboard can be used similarly to the ordinary blackboard or white board in a way such that an image can be optionally written on display sheet 1002 exposed at opening 1001a of box type frame 1001 and the image can be erased. In addition, by display surface image reading scanner 1005 and printer 1006, the image on display sheet 1002 can be printed on a paper surface and recorded.
Further, such an electronic blackboard has not only advantages which the blackboard and white board have, in that the display surface is large, there is no need for darkening the room, visibleness is excellent, and an optional part of the image can be easily written, erased and corrected, but also remarkable advantages in that the image on the display surface can be recorded on a paper surface and stored.
As mentioned above, the information board and the electronic blackboard which display a static image can be effectively used by utilizing the respective advantages. Further, they are advantageous image display devices from the viewpoint of the reduction of the consumption of paper and electric power.
However, in the above-mentioned recording principle of the information board, the toner needs to have magnetic properties. Therefore, the coloring of the toners in colors other than black is difficult, and thus, there has been a problem in that a color image cannot be formed.
Further, the above-mentioned electronic blackboard is not a device in which the image information transmitted from an external image input device, such as a computer or the like, is automatically written on the display sheet using image recording means, such as an ink-jet recording method or the like, but a device in which an optional image, such as a character, a figure or the like, is written on the display sheet in handwriting, and thus, this not suitable as a display device for a notice plate, advertisement plate and the like. In addition, with respect to this electronic blackboard, there has not yet been a product in which the image written once is automatically erased. Conventionally, some proposals have been made with respect to the invention of the electronic blackboard having image erasing means, and such invention is disclosed in, for example, Japanese Patent Application Laid-Open Nos. 61-9071, 5-597, 5-14564, 5-160940, 5-162494, 632095, 6-48091, 6-87295 and 6-245008. In the above-mentioned prior art documents, there is disclosed an invention wherein an image, such as a character, a figure or the like, is written on a recording medium (display sheet) in handwriting using writing utensils for electronic blackboard, and the image on the recording medium is wiped and erased using a device similar to the electrophotography sensitizing material cleaning device used in a copying machine, such as a cleaning fur brush, a rubber blade or the like. However, the writing of the image according to above prior art documents is done only in handwriting using writing utensils in a conventional manner.
In contrast, in Japanese Patent Application Laid-Open No. 5-58091, image writing which is performed automatically is disclosed. In this Japanese Patent Application Laid-Open No. 5-58091, by discharging the same ink as that in the pen used in the handwriting, i.e., ink for use in the marker pen for white board, from an ink-jet head, an image is formed on the display sheet automatically. According to this, it seems that the writing of an image on the display sheet can be performed automatically; however, actually, it is difficult to excellently discharge the above-mentioned ink for use in the marker pen for a white board from the ink-jet head, and thus, it is considered that it is also difficult to surely form an image. The reason why it is difficult to excellently discharge the above-mentioned ink for use in the marker pen for a white board from the ink-jet head is presumably that the ink viscosity is high. In addition, the above-mentioned ink for use in the marker pen for a white board is not designed so that it is discharged from the ink-jet head. Therefore, this ink does not have a satisfactory moisture property, and thus, this ink is likely to be too dry. As a result, non-discharge of a nozzle is likely to occur. As apparent from the above, for surely forming an image on the display sheet, it is necessary to use an ink which can be excellently discharged from the ink-jet head.
In the above-mentioned display device for displaying a static image for the purpose of advertisement, propaganda, notice and the like, it is desired that the device has functions not only as a stand-alone device placed in a meeting room like an electronic blackboard, but also as a display device which can be connected with a network, and that it is possible to successively display the information from a distant place through the network, and in a plurality of places.
Further, it is desired that not only can the image writing and erasing in accordance with the image information from an external image display device, such as a computer or the like, be performed, but also a color image can be displayed, and additionally, it is possible to display high quality image.
Thus, the present inventors have made experiments and studies on the image display device, as a system capable of displaying a color image, which comprises a recording medium similar to the electronic blackboard, ink-jet recording means and image erasing means, wherein an ink is discharged from the ink-jet recording means on the recording medium to display the image on the recording medium, and then, the image on the recording medium can be erased by the image erasing means.
The ink-jet recording method is a method in which the recording is performed by forming ink drops and allowing the ink to adhere to a recording medium, such as a pager, an OHP film or the like. The ink for ink-jet recording used in the conventional ink-jet recording method generally contains water as a main component, a dye or pigment mixed as a colorant, and further a water-soluble high-boiling point solvent, such as a glycol, for the purpose of prevention of the drying and the nozzle clogging and the like.
When, using such an ink for ink-jet recording, the recording is performed on the recording medium similar to the conventional electronic blackboard by the ink-jet recording method, a problem arises in that an excellent image formation is difficult because the above-mentioned ink for ink-jet recording is repelled on the recording medium. Further, also in Japanese Patent Application Laid-Open Nos. 8-106261 and 8-310078, the recording on an electronic blackboard using an ordinary ink for ink-jet recording is disclosed; however, by the inventions disclosed in these prior art documents, the above-mentioned problems also cannot be solved.
Herein, the reason why the above-mentioned ink for ink-jet recording cannot be excellently fixed on the recording medium similar to the conventional electronic blackboard is briefly explained. In general, as a recording medium used in the electronic blackboard, a display sheet obtained by laminating a fluorine compound system film on an opalescence white base film is used. (Generally, such a display sheet has a hard permeability.) When an image is written on this display sheet using a pen for electronic blackboard (hereinafter, referred to also as marker for white board), a resin film containing a releasing agent and a pigment remains on the display sheet after the moisture among the ink components is evaporated. Thus, when the writing is performed using a pen for electronic blackboard, the ink can be excellently fixed on the display sheet. Further, this resin film can be easily released from the display sheet, and thus, wiped and erased by a cloth, a felt, a sponge or the like. This is because the surface tension of the recording medium surface (display sheet surface) is set to be low so that the image on the display sheet is easily erased. On the other hand, when an attempt is made to fix an ink for ink-jet recording on the display sheet, an excellent image formation cannot be achieved due to the flowing of the ink. This is because, generally, the ink for ink-jet recording permeates into a recording medium (ink receiving layer), so that the ink is fixed on the recording medium. That is, the ink for ink-jet recording is designed so as to permeate into the recording medium. Therefore, when an attempt is made to fix the ink for ink-jet recording on the above-mentioned display sheet having a hard permeability, the ink cannot permeate into the display sheet because there is no ink receiving layer in the display sheet, and thus, the ink flows on the display sheet. For forming an image on the recording medium having a hard permeability, it is necessary that the ink be not the conventional ink which permeates into the recording medium but an ink which is fixed on the recording medium surface. It should be noted that when the retention property (fixing property) of the ink is enhanced to too high extent, in turn, the ink cannot be released from the recording medium. Therefore, the balance between the fixing property and the releasing property of the ink relative to the recording medium is important. Taking the above into consideration, an ink which can be fixed on a recording medium having a hard permeability, released from the recording medium after the fixing on the recording medium once, and discharged from ink-jet recording means is desired.
For the above-mentioned image display device in which an image can be recorded on the recording medium repeatedly and the image can be erased repeatedly, it is desired that not only can the ink forming the image be easily released from the recording medium, but also the ink is strongly fixed on the recording medium. That is, it is necessary to simultaneously satisfy the antithetical properties, i.e., the fixing property and the releasing property of the image.
In view of the above-mentioned problems, the present invention has been made, and an object of the present invention is to provide an image display apparatus and an image erasing method, by which the recording and the erasing of the image in accordance with the image information from an external image display apparatus, such as a computer or the like, can be performed.
Further, it is an object of the present invention to provide an image display apparatus and an image erasing method, by which a color image can be displayed by fixing an ink on a recording medium using ink application means, and, when it is desired to erase the color image, the color image on the recording medium can be erased by image erasing means, and additionally, it is possible to display a high quality image.
It is an object of the present invention to provide an image display apparatus and an image erasing method, in which the apparatus has functions not only as a stand-alone apparatus placed in a meeting room and the like, but also as a display apparatus which can be connected with a network, and it is possible to successively display the information of static images for the purpose of advertisement, propaganda, notice and the like from a distant place through the network, and further in a plurality of places simultaneously.
Further, it is an object of the present invention to provide an ink used in the above-mentioned image display apparatus.
For attaining the above objects, the image display apparatus according to the present invention is characterized in that it has the following construction.
Specifically, the image display apparatus of the present invention is an image display apparatus for displaying an image on a recording medium using an ink, comprising: ink application means for applying an ink containing a polymer onto said recording medium in accordance with image data; and image erasing means for erasing the image by coming in contact with the image formed on said recording medium by said ink application means and the subsequent separation, wherein, when the solubility parameter (SP value) of the polymer substance remaining on said recording medium after applying the ink is taken as SPp, the SP value of the substance constituting the surface of said recording medium is taken as SPm, and the SP value of the substance constituting the surface of said image erasing means is taken as SPc, said SPp, SPm and SPc satisfy the relationship: |SPpxe2x88x92SPm| greater than |SPpxe2x88x92SPc|.
Further, the image erasing method according to the present invention is characterized in that it has the following construction.
Specifically, the image erasing method of the present invention is a method comprising the steps of: contacting a substance for erasing an image with the image formed by applying an ink containing a polymer; and subsequently separating the substance for erasing an image from the recording medium, to thereby erase the image on the recording medium, wherein, when the solubility parameter (SP value) of the polymer substance remaining on the recording medium after applying the ink is taken as SPp, the SP value of the substance constituting the surface of the recording medium is taken as SPm, and the SP value of said substance for erasing an image is taken as SPc, said SPp, SPm and SPc satisfy relationship: |SPpxe2x88x92SPm| greater than |SPpxe2x88x92SPc|.
Further, the image display apparatus according to the present invention is characterized in that it has the following construction.
Specifically, the image display apparatus of the present invention is an image display apparatus comprising: an ink-jet head capable of discharging an ink containing a polymer emulsion; a recording medium having a hard permeability for said ink, for displaying an image made of said ink; and an ink release means capable of releasing said ink from said recording medium by coming in contact with the ink on said recording medium and the subsequent separation, wherein the substance constituting the surface of said ink release means is selected so that the attractive force exhibited between said ink and the surface of said ink release means is stronger than that exhibited between said ink and said recording medium.
Further, the ink according to the present invention is characterized in that it has the following construction.
Specifically, the ink of the present invention is an ink used in an image display apparatus for displaying an image on a display sheet by discharging an ink from an ink-jet recording head, wherein said ink comprises at least one selected from the group consisting of a glycol and an alcohol, a polymer emulsion, and a pigment, wherein said ink contains 0 to 10% by weight of said glycol, 0 to 20% by weight of said alcohol, 0.001 to 0.5% by weight of said polymer emulsion, and 1 to 10% by weight of said pigment, based on the total weight of said ink.
It should be noted that the SP value in the present specification means a solubility parameter, and the solubility parameter can be used as an index for an adhesive force. This solubility parameter is defined in xe2x80x9cMcGraw-Hill Dictionary of Scientific and Technical Termsxe2x80x9d (edited by Editorial Committee of McGraw-Hill Dictionary of Scientific and Technical Terms, published by The Nikkan Kogyo Shinbun Ltd., Japan). Further, in xe2x80x9cAdhesive Handbookxe2x80x9d (edited by Japan Adhesive Society, published by The Nikkan Kogyo Shinbun Ltd., Japan) and the like, there is a description reading xe2x80x9cThe closer the SP values of substances, the easier the adhesion between the substances.xe2x80x9d
Further, the SP value used in the present specification is, as described in pages 7 to 23 of the above-mentioned xe2x80x9cAdhesive Handbookxe2x80x9d, defined by the following formula:
SP=(C.E.D)xc2xd=(xcex94Hxe2x88x92RT/V)xc2xd
wherein:
C.E.D is a cohesive energy density (cal/cm3);
xcex94H is heat of vaporization (cal/mol);
V is a molar volume (cm3/mol);
R is gas constant (cal/degxc2x7mol); and
T is an absolute temperature (degxc2x7K).
(Note that xe2x80x9cdegxe2x80x9d is an abbreviation of degree.)
It should be noted that the xe2x80x9cpolymer dispersionxe2x80x9d in the present specification means a state such that a polymer is dispersed in a liquid, and hereinafter, the xe2x80x9cpolymer dispersionxe2x80x9d is referred to also as polymer emulsion.
In addition, the above-mentioned polymer means a substance having a molecular weight of 1,000 or more in the present specification.
Further, the xe2x80x9crecording medium having a hard permeabilityxe2x80x9d in the present specification means a recording medium having water permeability P (g/m2, 24 hr) which satisfies the relationship: 1 less than P less than 25, wherein the water permeability can be measured in accordance with JIS K5400 (1990) 8.16.